1. Technical Field
The present invention relates to a path display apparatus. More specifically, the present invention relates to a path display apparatus that displays the path of the tip point of a tool taking into account correction data such as backlash correction and pitch error correction.
2. Description of Related Arts
Numerical control apparatuses are commonly used to drive a plurality of motors, drive a table via a ball screw and position a tool in a desired position. Such a mechanism produces mechanical backlash and variations in the pitch of the ball screw (pitch error).
Consequently, to reduce the influence of such backlash and pitch error, correction data such as backlash correction and pitch error correction is generated. When controlling the tip portion of a tool, correction of the tool length and correction of the tool diameter are used as correction data depending on the machining conditions.
FIG. 8 is a block diagram relating to the position control of a motor, for explaining the handling of correction data. As illustrated in FIG. 8, correction data C that is generated is added to a position command P of the motor, to generate a corrected position command Pc. Then, a position feedback Pf that is detected by a detector D of the motor M is subtracted from the corrected position command Pc and the subtraction result is output to a motor controller, and by this means, the motor M is controlled.
As described with reference to FIG. 8, it is common that correction data is superimposed on a position command of a motor, which is controlled. For example, Japanese Patent Laid-Open Publication No. 3-58102 discloses improving the accuracy of positioning by changing the amount of backlash correction according to the feeding direction and feeding speed.
FIG. 9A is a diagram illustrating a command path that is calculated from a position command of an end of the motor when backlash correction is added to a position command for a circular arc, and FIG. 9B is a diagram illustrating its feedback path. The circular arcs illustrated in these drawings correspond to the position command P of the motor. Furthermore, the command path indicated by the broken lines in FIG. 9A corresponds to the corrected position command Pc, and the feedback path indicated by the broken lines in FIG. 9B corresponds to the position feedback Pf. In these drawings, since the correction data C (backlash correction) is added to the position command P, the command path (FIG. 9A) and the feedback path (FIG. 9B) have shapes that deviate from the circular arcs corresponding to the position command P.
Furthermore, FIG. 9C is a drawing that is similar to FIG. 9A and that illustrates a command path calculated from a position command of an end of the motor when pitch error correction is added to the position command for the circular arc, and FIG. 9D is a drawing that is similar to FIG. 9B and that illustrates its feedback path. Furthermore, the command path illustrated in FIG. 9C corresponds to the corrected position command Pc, and the feedback path illustrated in FIG. 9D corresponds to the position feedback Pf. In these drawings, since the correction data C (pitch error correction) is added to the position command P, the command path (FIG. 9C) and the feedback path (FIG. 9D) deviate from the circular arcs corresponding to the position command P.
In this way, when the correction data C is superimposed on the position command P of the motor, the tool path to be calculated based on the corrected position command Pc does not match the path corresponding to the position command P. In other words, these paths differ from each other based on the correction data.
Compared to a mechanical error, a transient error due to the delay of the servo is significant. Consequently, when checking the response delay of the motor in the actual machine tool to which correction data is applied, or when adjusting the servo, it is necessary to temporarily invalidate the correction data. In other words, the path is checked by making the path calculated from the corrected position command Pc match the path calculated from the position command P of the motor. However, such a technique is very complex and time-consuming for an operator.
The present invention has been made in view of the above backgrounds, and it is therefore an object of the present invention to provide a path display apparatus that is capable of checking the response delay of the motor and performing servo adjustment using even a simpler method even when using an actual machine tool to which correction data such as backlash correction and pitch error correction is applied.